Venous valves can improve the severe symptoms of patients with post thrombotic syndrome suffering from swelling and ulcerations of their legs. This condition can be caused by stenosis and occlusions of the veins and deterioration of the venous valves. Certain techniques have been developed to surgically restore incompetent valves or to implant devices that aid in such restoration. However, there remain many situations in which a valve is compromised to the extent that these options are not effective and valve replacement must be considered. By replacement of the venous valves, the capillary venous pressure can be decreased in this group of patients eventually improving their condition.
Venous valves have been proposed that consist of a stent device combined with a moving valve being mounted to the stent. However, stents can reduce the effective orifice area of the valve which increases the transvalvular pressure gradient. A further drawback to this valve is that a stent has fixed dimensions and remains in contact with the total circumference of the inner venous surface which, therefore, can irritate a large amount of the venous wall, especially the endothelium. This can be followed by intimal hyperplasia and thrombosis. Further, trauma to the wall of the vein is induced by shear stress between the wall components and the stent, because the venous diameter changes normally. The failure to accommodate growth of the patient is particularly problematic for children undergoing valve replacement, for example. A continuing need exists, therefore, for improvements in valve replacement systems and in methods for placement of such valves.
The present device relates to an implantable valve having a valve element that is attached to region of the a vessel wall with a tissue connector. The valve can be placed within a body lumen using endoluminal techniques such as a percutaneous catheter. The valve element can be formed with a biocompatible material such as plastic (e.g., PTFE) with a generally oval or circular shape. Materials such as textile fabric and donor tissue, such as fascia lata, for example, can also form the valve element. The valve element rotates relative to a position on the vessel wall where the connector is located and moves between open and closed positions to permit fluid flow in one direction and prevent fluid flow in the opposite direction.
The valve element can have a curved surface, with the generally convex side of the valve element facing against the preferential direction of flow of fluid within the lumen in which the valve is placed. The opposite side of the valve element can consequently have a concave shape. A preferred embodiment of the valve element uses a frame to reinforce the element. The periphery is preferably soft, however, to prevent vessel wall damage. The valve element generally has a diameter in a range between 2 mm and 45 mm, and a thickness between 0.2 mm and 3.0 mm.
The valve element or leaflet is attached to a stationary base such that the leaflet can move or rotate relative to the base. The base is attached to the vessel wall with a connector such as a pin, a screw, a staple, and/or an adhesive. In the event that open implantation is performed, a surgical suture can also be used as the connector. The connector can be used to attach the valve element to the base. In a preferred embodiment the base and the valve element can be formed as a unitary structure in which the valve element has a hinge region to provide for rotation of the valve element relative to the base.
A preferred embodiment of the invention uses a catheter to position the valve at a site within a body lumen and to attach the valve to a point on a wall of the lumen. The catheter can employ a system that attaches the valve to the vessel wall in which the catheter has a driver at the distal end that attaches the connector to the lumen wall. The catheter can have a guide that is used to position the distal end of the catheter, the guide and/or the connector for proper anchoring of the valve to the lumen. The guide can be a cord that extends through another catheter lumen or a sheath around the catheter that is connected at one end to the distal end of the catheter such that the user can mechanically pull the cord to bend the distal end of the catheter and consequently move the connector from one side of the lumen to the opposite side so that the portion of the connector that is to penetrate the vessel wall is properly oriented so as to be driven and securely attached. A release mechanism to detach the system from the valve and/or connector after placement can also be used.
Alternately, the valve can have a base with a connector to attach the valve to a lumen wall and a tubular wall connected to the base. The tubular wall has a proximal end with a proximal opening and a distal end with a distal opening. When implanted into a lumen, flow from the distal end to the proximal end forces the tubular wall into an open position thereby allowing flow through the tube while flow from the proximal end to the distal end forces the tubular wall into a closed position, thereby preventing flow in this direction. The valve can be shaped as a wedge shaped tube or as a curve shaped tube. The curve shaped tube can include a crease portion which allows the tube to collapse in the presence of back flow, thereby preventing back flow from entering the tube. The valve can be made from a silicone material.
The valve can also have a base with a connector to attach the valve to a lumen wall, a leaflet and a hinge connecting the base and the leaflet. The leaf or leaflet can be formed with an oval shape. The leaflet can have a concave shape. The leaflet can also have a rim and a center portion wherein the rim is thinner than the center portion. The valve includes a reinforcement frame which can be a metal filament. The valve can include a fabric material connecting the leaflet and the base. The fabric material can include a first layer and a second layer. A reinforcement member can be located between the first layer and the second layer.